1. Technical Field
The present invention relates to, in general, a metal halide lamp and a lighting apparatus and, in particular, a metal halide lamp with a low color temperature having a ceramics arc tube and a lighting apparatus using the metal halide lamp.
2. Background Art
Metal halide lamps are used not only for the base lighting as a down light but also for the spot lighting for directly illuminating items in a commercial facility such as the store lighting. In the spot lighting, higher optical characteristics is required than in the base lighting. Specifically, the required characteristics is that the Ra (general color rendering index) is 90 or more, the R9 (special color rendering index) is 50 or more, the color temperature is 2800 to 3700 K, and the Duv (illuminant color (tinge)) is −5 to 0.
Further, the increased efficiency is desired for the spot lighting as well as the base lighting in terms of energy saving.
For example, while the efficiencies of the commercially available lamps are 90 ml/W for rated power 35 W, 95 ml/W for 70 W, and 100 ml/W for 100 W, the demanded efficiencies are increased up to 95 ml/W for rated power 35 W, 100 ml/W for 70 W, and 110 ml/W for 100 W.
In general, in the ceramic metal halide lamp, there is a tradeoff relationship between high color-rendering and high efficiency, and therefore it has been difficult to improve both of them at the same time.
Patent document 1 discloses a ceramic metal halide lamp with the low color temperature type (2800 to 3700 K). Patent document 1 discloses that the light emission material (halogen iodide) sealed in the lamp contains a composition ratio of 0.5 to 4 mol % of cerium or praseodymium (for example, 2 mol % of cerium), a composition ratio of 35 to 45 mol % of sodium (for example, 35 mol %), a composition ratio of 40 to 60 mol % of calcium (for example, 54 mol %), 2 mol % of thallium, and a composition ratio of 2 to 10 mol % of rare earth metal including dysprosium, thulium, or holmium (for example, 7 mol % of the rare earth metal comprising the above three materials). It is disclosed that the above design results in that the efficiency is 94 lm/W, the Ra is 90 or more, the R9 is 40 or more, and the lower limit of the Duv value is −10, and this specification can be applied to the lamp of the rated power of 20 to 300 W. In particular, it is generally known that the composition ratio of calcium is increased in order to improve the R9, and the above composition is based on this knowledge.